usb gadget: RNDIS cleanups

Some cleanup to the RNDIS code:

 - Minor bugfix:  rndis_unit() is supposed to put the link into the
   RNDIS_UNINITIALIZED state, which does not mean "unused".  There's
   a separate method to stop using the link.  (Bug doesn't affect
   anything right now because of how the code is used.)

 - Reduce coupling between RNDIS code and its user(s), in preparation
   for updates in that code:

    * Decouple RNDIS_RESPONSE_AVAILABLE notifications from net_device
      by passing just a void* handle.  (Also, remove the unused return
      value of the notification callback.)
    * When it needs a copy of net_device stats, just ask for it

 - Remove unused/untested code backing various never-used OIDs:

    * RNDIS_PM, RNDIS_WAKEUP ... "should" get implemented, but the
      relevant docs were unclear, ambguous, and incomplete.  Someone
      with access to the Hidden Gospels (maybe in the EU?) might be
      able to figure out what this should do.
    * RNDIS_OPTIONAL_STATS ... as the name suggests, optional.  Never
      implemented in part because not all the semantics were clear.
    * OID_GEN_RNDIS_CONFIG_PARAMETER, which has been #if 0 forever.

 - A few small whitespace fixes

Plus switch the VERBOSE symbol over to the newer VERBOSE_DEBUG style.

There should be no functional changes because of this patch; it's a
net source code shrink (because of the dead/unused code removal) and
a small object code shrink (a couple hundred bytes on ARMv5).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>